There is a demand for cutting of metals, stone, and other materials for such things as mining, salvage, rescue work, infrastructure development, and environmental remediation. Problems with flammability and material properties can hamper conventional cutting technologies. Non-limiting applications for safe vehicle mounted abrasive entrainment waterjet cutting systems include cutting pipeline; clearing passageways through rocks for communications and electrical power infrastructure; disposal of discarded military munitions (DMM), etc. Oxy-arc, oxy-fuel, oxy-hydrogen and arc cutting can be used to cut steels in non-hazardous locations. Mechanical drills and cutting tools, such as circular, ring, band, wire, and abrasive saws can also be used with varying degrees of success. None of these methods are easy to perform remotely and all have limitations that restrict their use. They are also generally hazardous to use around flammable or explosive materials, which are all too frequently found underground.
One conventional method of disposing of discarded military munitions is to detonate them in-situ using highly skilled personnel to place the necessary explosive charges. Unfortunately, serious contamination of the environment can occur with the dispersal of unreacted toxic chemicals. Abrasive entrainment waterjets have the potential of providing a safe and environmentally friendly alternative to conventional cutting technologies if certain obstacles can be overcome. Such obstacles include being able to feed a substantially steady flow of high-pressure water to the cutting head in certain remote locations.
The word “waterjet” is an ambiguous term used to broadly describe essentially any process that expels a liquid, regardless of pressure or fluid chemistry, through an orifice to form a fluid jet. The wide-ranging term of “waterjet” is used to include everything from low-pressure dental hygiene equipment to high-pressure systems incorporating abrasives that can cut through thick hardened steel and rock. In addition, a further confusion is introduced as the use of the word “water” in the term “waterjet” does not limit the application's use to only pure water (H2O) as the fluid in the waterjet. In this context the word “water” can imply any fluid, any solution, and any solid material that will flow through an orifice under pressure or any gas that liquefies under pressure, such as ammonia, to form what should more precisely be termed a “fluid” jet, but by convention is defined in the trade as a “waterjet.”
Waterjets are fast, flexible, reasonably precise, and are relatively easy to use. They use the technology of high-pressure water being forced through a small hole, typically called the “orifice” or “jewel” which is typically about 0.007″ to 0.020″ in diameter (0.18 to 0.4 mm), to concentrate an extreme amount of energy in a small area. The restriction of the tiny orifice creates high pressure and a high-velocity jet. The inlet (process) water for a pure waterjet is typically pressurized between 20,000 psi (138 MPa) and 60,000 psi (414 MPa). This is forced through the orifice or jewel which creates a very high-velocity, very thin jet of water traveling as close to the speed of sound.
Abrasive slurry waterjet, also known as an abrasive suspension jet, typically uses a hopper filled with abrasive, water, and a slurrying or suspension agent. This combined mixture is then pressurized and forced through the orifice of the waterjet cutting head. The abrasive slurry system must keep the abrasive in constant suspension, such as with use of chemical additives or by mechanical means, in order to prevent the abrasive from dropping out of suspension in the piping which leads to plugging and disabling of the system. Likewise, the flow of pressurized abrasive and water slurry mix is highly erosive to piping, valves, and fittings used in the system. In addition, one or more large pressure vessels must typically be used to contain a sufficient amount of abrasive slurry for cutting. Consequently, an abrasive slurry system is typically limited in pressure to approximately 140 MPa and normally operates at pressures closer to about 70 MPa.
An abrasive entrainment waterjet uses a high velocity fluid jet, formed by pressurized water passing through an orifice (jewel) of the cutting head resulting in a partial vacuum in a mixing chamber downstream of the orifice that aspirates and entrains abrasive particles that are introduced into the mixing chamber and into the fluid jet. Abrasive entrainment waterjet technology has several advantages over abrasive slurry waterjet technology. For example, it is more reliable; it requires less maintenance; it is able to operate at internal system pressures up to about 1,000 MPa or more; it can operate in a continuous mode rather than in a batch mode; it doesn't require expensive chemical additives; and it is able to operate with significantly lower abrasive consumption.
Waterjet technology has been used above ground and underwater for cutting metals and stone. For example, waterjets were taught as being effective in underwater mining operations. See Borkowski, P. and Borkowski, J. (2011). “Basis of High-pressure Water Jet Implementation for Poly-metallic Concretions Output from the Ocean's Bottom,” Rocznik Ochrony Środowiska Selected full texts, 13, ppg. 65-82. An abrasive slurry system is taught as being capable of operating on remotely operated vehicles. Miller (U.S. Pat. No. 6,681,675) teaches using an abrasive entrainment waterjet on vehicles tethered to a stationary high-pressure water intensifier pump by a long hose. Unfortunately, the long hose limits the functional distance the waterjet can operate from the intensifier pump as well as severely limits the maneuverability of the waterjet carrying vehicle. Manders (U.S. Pat. No. 7,600,460) teaches a dedicated waterjet vehicle carrying a separate engine-pump combination for removing soil for exposing and defeating landmines.
While the art teaches the possibility of using waterjet technology for above or below ground cutting, there is still a need in the art for solving serious problems that exist and which must be overcome before such technology can be used commercially.